1. Technical Field
The instant disclosure relates to an integrated circuit device, in particular, to a transmission line in the integrated circuit device.
2. Description of Related Art
Conventional transmission lines in CMOS process are capable of carrying low frequency alternating current and audio signals. The transmission lines utilize specific structure and methods for performing impedance matching and thus the electromagnetic signals carried can reach the receiver end with the smallest reflection and power loss. Most transmission lines have a significant characteristic in that they have uniform cross sections along the lengthwise direction, thereby having uniform impedance which is referred to as characteristic impedance which prevents reflection. There are many forms of transmission lines such as parallel lines (stepped, twisted pair), coaxial cable, stripline and microstrip. The frequency of the electromagnetic wave is inversely proportional to the wavelength thereof. When the length of the cable is equal to the wavelength of the transmission signal, there is a need for the use of a transmission line.
Transmission lines are also used in integrated circuit devices, generally as coplanar waveguide structures having signal line and the ground line that are parallel, or as stripline structures in which the transmission lines are surrounded by the ground lines. However, in order to maintain the sufficiently low characteristic impedance, the transmission lines must occupy sufficiently large space in the structure. Due to the integrated circuit devices becoming smaller in size, and the parasitic capacitance becoming larger, the difficulties in the designing of the transmission lines in the integrated circuit devices are increasing.